Abstract

The polychaete Hediste diversicolor is characterised by a high degree of genetic structure among populations. The genetic differentiation has been related to the presence of cryptic species, corresponding to Atlantic and Mediterranean lineages whose divergence may have been driven by vicariance and/or selection. In this study we used DNA inter-simple sequence repeat (ISSR) markers to validate the genetic structure in nine populations from the north-western Mediterranean. We also analysed patterns of genetic differentiation among Mediterranean and Atlantic samples to assess the occurrence of further cryptic species in the north-western Mediterranean . We compared our results with previous mitochondrial DNA data to assess whether nuclear and mitochondrial genetic patterns were consistent. Analysis of ISSR banding patterns showed (1) a geographical structuring within the north-western Mediterranean, and (2) a sharp genetic differentiation between Atlantic and Mediterranean groups of populations, confirming the findings from previous mitochondrial DNA survey. The pattern of genetic variability found in the north-western Mediterranean is unlikely to reflect the occurrence of cryptic species in this area. On the other hand, our results are consistent with the occurrence of two cryptic species in the Mediterranean and Atlantic, whose genetic differentiation may have been driven by vicariance. Finally, this study further highlights the usefulness and effectiveness of ISSR markers for monitoring genetic diversity in aquatic invertebrates.